Electromagnetically actuated control valves are widely used in fuel injectors and timing fluid and injection fuel metering system for precisely controlling the timing and metering of the injection fuel and timing fluid. Precise control of the timing and metering of fuel and timing fluid is necessary to achieve maximum efficiency of the fuel system of an internal combustion engine. In addition, valve designers continually attempt to reduce the size of the control valves to reduce the overall size and weight of the engine and permit the control valves to be easily mounted in a variety of locations on the engine without exceeding packaging restraints.
Another concern of valve designers is valve seat wear and valve bounce. High impact forces of the valve element against a valve seat causes valve seat beating and excessive wear. Moreover, when the valve impacts the valve seat at a high velocity, the valve tends to bounce off the seat adversely affecting the control of fluid flow and causing additional valve seat wear.
Control valves are often operated by a solenoid type actuator assembly. For example, U.S. Pat. No. 4,946,107 to Hunt discloses an electromagnetic fuel injection valve including a coil mounted on a bobbin, a core or stator extending into one end of the bobbin and an armature valve extending into an opposite end of the bobbin. One end of the armature valve includes a valve ball for engaging a valve seat while the opposite end abuts a distal end of the stator when the valve is in the open position. However, the core or stator is of the solid core magnet design which is sensitive to changes in supply voltage resulting in inadvertent movements of the valve and undesirable changes in fluid flow. In addition, when the armature valve contacts the distal end of the stator, or a shim mounted on the stator, the residual magnetism in the stator may cause the armature to be held against the stator or shim disadvantageously resulting in erratic valve performance. Although the shim may reduce the holding effect of the residual magnetism, the shim adds unnecessary costs to the valve. Also, the armature valve is guided through its reciprocal movement by a guide piece separate from the part which stops outer movement of the armature valve, i.e. stator, thereby requiring an excessive number of parts. U.S. Pat. Nos. 4,742,964; 5,301,874; 5,322,260; and 5,626,325 disclose other solenoid operated valve assemblies suffering from the same disadvantages as the actuator/valve disclosed in Hunt.
U.S. Pat. No. 5,626,325 to Buchanan et al. does disclose a solenoid operated control valve including a compliant web portion for supporting the valve seat and allowing the valve seat to flex upon contact by the valve element thereby mitigating problems of seat beating. However, the valve element contacts the valve seat at an unreduced impact velocity which may result in valve bounce and possibly excessive valve seat wear over time.
U.S. Pat. No. 5,513,832 to Becker et al. discloses a solenoid valve having a coil spring attached to one end of an armature and a spring adjustment screw abutting the coil spring, wherein the spring adjustment screw threadably engages a central threaded bore in the solenoid valve housing to allow the solenoid valve to be externally calibrated. Becker et al. further discloses a bearing which guides the longitudinal movement of a pin/armature assembly to maintain a relatively uniform radial air gap between the armature and a magnetically conductive tubular body. A stop ring is used to limit the movement of the valve into an open position. However, the stop ring is formed separate from the bearing guide resulting in an excessive number of valve parts and increased costs. Moreover, the armature is positioned within the inner radial extent of the coil assembly creating an unnecessarily wide assembly.
U.S. Pat. No. 3,861,643 is noted for disclosing a magnetic control valve having a center core of magnetic material extending through the center of the solenoid coil. A magnetic air gap is formed between the inner end of the center core and the armature. However, during operation, the armature may contact the center core since no other stop is provided. Repeated contact between the center core and the armature will result in excessive wear and possibly unacceptable damage to the armature which is normally formed of a very soft magnetic material. Moreover, the center core is a solid core magnet which is sensitive to changes in supply voltage resulting in inadvertent movements of the valve and undesirable changes in fluid flow.
Consequently, there is a need for a compact, inexpensive electromagnetic actuator assembly for a valve and an improved valve assembly capable of effectively controlling valve movement throughout all valve operating conditions.